This invention relates to increasing the molecular weight of a polyamide by using a designated catalyst.
U.S. Pat. No. 3,763,113 describes a process for the amidation of nylon 66 using as catalysts phosphonic acids of the formula: EQU R(PO.sub.3 H.sub.2).sub.n
wherein n is 1, 2 or 3, and R is a mono-, di-, or trivalent organic radical depending on the value of n. Example 10 shows the use of a weakly activating substituent (p-PO.sub.3 H.sub.2 C.sub.6 H.sub.4 --). The results, however, as stated in the patent clearly show that this example gives results which are only slightly better than phenylphosphonic acid as measured by the relative viscosity of the final product. There is no indication from the Examples that moderate or strongly activating groups would have a significant effect on the rate of reaction.
U.S. Pat. No. 3,365,428 describes a process for the amidation of nylons using as catalysts phosphinic acids of the formula: EQU RR'PO.sub.2 H
wherein R is an aryl or alkaryl radical, and R' is hydrogen or an alkyl, aralkyl, aryl or alkaryl radical. Example 8 shows the use of the weakly activating substituents CH.sub.3 -- and C.sub.6 H.sub.5 --; as stated in this Example, the results as obtained are similar to the results obtained using a similar amount of phenylphosphinic acid. There is no indication from the Examples that moderate or strongly activating groups would have a significant effect on the rate of reaction.
Thus a need still exists for catalysts which will effect the rate of reaction for increasing molecular weight. Greater throughput, or for the same reaction time, production of a higher molecular weight material would result in a higher strength material.